Natural draft low swirl burner

ABSTRACT

A new design for a low swirl burner is disclosed in which natural draft rather than a motorized pump is used to move a fuel-air mixture through the burner. This new design enables the burn off of gas at refineries in an environment where electric motors cannot be used because of the potential for sparks, which could trigger explosions. Additional modifications to the burner, including the introduction of flue gas to the burner allows for the reduction of NOx gas to meet current emission control targets, without the need for further post combustion emission control systems.

CROSS REFERENCE TO RELATED CASE

This application claims priority to PCT Application PCT/US2012/032526,filed Apr. 6, 2012, which in turn claims priority to U.S. ProvisionalApplication Ser. No. 61/475,159 filed Apr. 13, 2011, which applicationis incorporated herein by reference as if fully set forth in theirentirety.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made with government support under Contract No.DE-AC02-05CH11231 awarded by the U.S. Department of Energy to theRegents of the University of California for the operation and managementof the Lawrence Berkeley National Laboratory. The government has certainrights in this invention.

FIELD OF INVENTION

The present invention is directed at energy efficient burners withminimal environmental impact. This invention relates generally to gasburners, and more particularly to burners using fuel that is premixedwith air or other oxidizers. Further this invention relates to the flamestabilization of gas burners and to burners that minimize the formationof oxides of nitrogen (NO_(x)). Stabilized flame burners are used formany heating purposes, including process heating and heating of air andgas streams in ducts. This invention relates to low swirl burners, andmore particularly to an improved low swirl burner for low emissionflames in which fuel pressure is utilized in a way that allows operationof the unit without the need of electric fans or blowers. Further thisinvention relates to natural draft burners.

BACKGROUND OF THE INVENTION

Existing natural draft burners are not based on the low swirl combustionconcepts and have high emissions. Other natural draft burners designedfor a specific industrial process, e.g. process heaters in oilrefineries can encounter noise issues and have limited stability. As aresult, users typically may need to use post-combustion emission controlmethods such as selective catalytic reduction to reduce emissions oftheir combustion systems to acceptable levels.

Another drawback with the burners currently in use in refineries, forexample, is that electric fans or blowers which would otherwise be usedare not, due in part to the risk of sparking, making their useundesirable or infeasible. Most commonly, natural draft burners utilizea fuel jet in a venturi to entrain and premix combustion air. Amechanical flame holder is located in the flow downstream of theventuri. The flame anchors on the flame holder and consumes the fuelthat is partially mixed with the air stream. The outer annular regionaround the flame holder can be fuel-depleted and may not sustain theflame. Since the flow in the center region may somewhat fuel-richrelative to the mixtures used in low NOx burners, the flame generatesrelatively high levels of NOx. In U.S. Pat. No. 4,419,074, multiple fueljets are used to improve the air-fuel mixing, but the assembly uses amechanical flameholder. NOx emissions from the design given in U.S. Pat.No. 4,419,074 exceed the levels required to satisfy the most stringentemissions requirements now promulgated.

The low swirl burners described in earlier U.S. patents (U.S. Pat. Nos.5,735,681 and 5,879,148) relied on mechanically driven systems to feedair into the burner. In the present invention, mechanically drivensystems are not utilized. In the present, fuel pressure is used toentrain combustion air at the inlet, mix the fuel and air, and drive theair through the burner. In addition, the appropriate swirl pattern inthe flow out of the burner may be created by mechanical vanes,appropriately angled fuel jets, or other devices that interact with theair-fuel flow in a way to create a swirling flow exiting the device.

The swirling flow pattern coming out of the device has a rotation in aplane normal to the axis of the flow. This flow pattern can be describedby a non-dimensional swirl number, S, which is defined as the ratio ofaxial flux of angular momentum to the axial flux of linear momentumdivided by the nozzle radius.

s=∫ ₀ ^(R) Uwr ² dr/R∫ ₀ ^(R) U ² rdr  [1]

S is described by equation (1), where R is the burner radius, and U andw are the mean axial and tangential components, respectively, of theflow velocity exiting from the swirl generator. The equation can bemodified for cases in which the swirling action is generated byappropriately oriented jets or by mechanical vanes.

In the case of the hub vane swirler design commonly used in swirlingburners, equation (1) reduces to:

$\begin{matrix}{S = {\frac{2}{3}\tan \; \alpha \; \frac{1 - R^{3}}{1 - R^{2} + {\left\lbrack {m^{2}\left( {{1/R^{2}} - 1} \right)}^{2} \right\rbrack R^{2}}}}} & \lbrack 2\rbrack\end{matrix}$

where R is the ratio of the radii of the central hub and the fullswirler assembly, the angle α is the exit angle of the swirl vanesrelative to the bulk flow axis, and m is the ratio of the mass of thenonswirling center flow to the mass of the outer swirling flow.

The rotating flow causes the gases to expand radially outward afterleaving the exit tube of the device. This expansion causes a decrease inthe axial velocity of the flow. There is a well-defined axial velocitygradient from the exit of the burner as the flow spreads out. Premixedair-fuel blends burn with well-defined flame speeds, and the flame willsettle at the location where the velocity out of the burner matches theflame speed. The characteristic flow pattern created by the low swirlburner provides an excellent flame stabilization mechanism.

Other burner designs that utilize premixed air and fuel rely on amechanical component (flame holder) and/or a highly swirling flow tostabilize the flame. These designs create a recirculation zonedownstream of the burner exit. The flame stabilizes in the recirculationzone due to the burning gases in the recirculation zone continuouslyigniting the incoming air-fuel mixture.

The production of NOx in the flame and exhaust of burners with premixedair and fuel is very dependent on the flame temperature, which in turn,is dependent on the air-fuel ratio. A stoichiometric air-fuel mixture,in which all of the fuel and oxidizer are consumed in the combustionprocess, generates the maximum flame temperature. Lower flametemperatures occur at both rich conditions where there is residual fuelin the exhaust and at lean conditions where there is residual oxygen oroxidizer in the exhaust. In most conditions, it is undesirable tooperate at rich conditions, since residual fuel can create additionalair pollution. To achieve very low (<10 ppm) NOx in the exhaust gas, itis necessary to create a very lean air-fuel mixture to establish a flametemperature with low NOx production. At lean conditions, it is importantto mix the air and fuel well before it burns. Locally rich zones in theair-fuel mixture will burn at a higher flame temperature and generateexcessive quantities of NOx. This behavior will prevent a low NOx burnerfrom achieving its intended NOx emission levels.

DEFINITIONS

Flashback: The circumstance in which the flame front burns back to theexit port of the fuel line from the flame stabilization point.

Fuel mixture: The mixture of one or more types of fuel.

Fuel-air mixture: The mixture of one or more types of fuel combined withoxygen-containing fluid such as air, where said mixture provides thereactants for combustion.

Premixed burner: A burner in which the fuel is mixed with air oroxygen-containing fluid before entering the flame zone.

Flame speed: The rate at which flame reactants are consumed incombustion.

Blowout: The circumstance in which the fuel mixture velocity exceeds theflame speed and thus extinguishes the flame.

Equivalence ratio: Measures the departure from a stoichiometriccombustion reaction. It is the ratio of fuel to available oxygen dividedby the ratio of fuel to stoichiometric oxygen. It is designated by φ.For example, for methane,

φ=[CH₄]/[O₂]_(actual)/[CH₄]/[O₂]_(stoichiometric)

where stoichiometric conditions are CH₄+2O₂=CO₂+2H₂O

Fuel rich conditions: φ>1

Fuel lean conditions: φ<1

Flame temperature: The temperature of the hottest part of the flame.

Axial flow: Flow that is parallel to the long axis of the burner body.

Radial flow: Flow that is perpendicular to the long axis of the burnerbody.

Rotational flow: Flow that rotates around the long axis of the burnerbody, in a plane normal to the axial fuel flow, also called tangentialvelocity.

Recirculation: Flow that changes from parallel to antiparallel to thelong axis of the burner body, also called flow reversal

SUMMARY OF THE INVENTION

By way of the present invention, we have developed a low swirl burnerthat can be powered by the fuel pressure alone, without the need forelectric fans or blowers, while at the same time reducing residualoxygen content to 3% or less, along with low levels below 10 ppm NOx.The energy stored in the fuel as a result of its pressurization is thusused to induce (entrain) air to flow along with it, and mix with thefuel. By minimizing the backpressure of the low swirl design andoperating with sufficient fuel pressure, stable operation of the lowswirl burner is achieved.

In an embodiment of the invention, the burner inlet geometry has beenmodified to entrain flue gas (exhaust gas) into the air-fuel mixturethat feeds into the low swirl burner. The flue gas acts as a diluent toreduce flame temperature and thus NOx (nitrogen oxides) emissionsproduced by the flame. This allows the burner to operate moreefficiently (at low excess air) while satisfying air quality regulationsthat limit release of NOx in the exhaust.

In an embodiment of the invention, an air entrainment system driven byone or more jets of fuel either combined with a suitable mechanicalswirler or configured with an appropriate geometry so as to create awell-mixed fuel-air blend and establish a flow pattern with anappropriate swirl number that is associated with the low swirl burnerdesign. One embodiment of the invention incorporates a jet-drivenventuri matched to a vane swirler assembly. The swirler configuration isconfigured to minimize the backpressure to the flow out of the venturiso as to maximize the velocity out of the burner assembly. The swirleris also configured to optimize the non-dimensional swirl numberassociated with the exiting flow. Another embodiment of the inventioncan incorporate multiple venturis to feed the inlet of a single swirler.This configuration is similar to the design described above, with theadditional advantage of having multiple venturis to allow the assemblyto be fabricated in a more compact fashion.

Another embodiment of the invention incorporates one or more fuel jetsoriented axially and radially in such a manner to establish a suitableswirl number and the characteristic flow pattern of the low swirl burnerat the exit. The jet orientation may differ from the air jet orientationof the original low swirl burner design. The fuel jets optionally feedventuris to optimize air entrainment.

Another embodiment of the invention involves modification of an airamplifier (a device that uses the Coanda effect to increase the overallflow rate of the supply gas) with vanes or patterns in the interiorwall, and optionally, a central structure, to establish a suitable swirlnumber and the characteristic flow pattern of the low swirl burner atthe burner exit.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with respect to particular exemplaryembodiments thereof and reference is accordingly made to the drawings inwhich:

FIG. 1 illustrates a natural draft slow swirl burner apparatus accordingto an embodiment of the invention.

FIGS. 2 a and 2 b are a cross sectional views of two alternative designsfor the natural draft low swirl burner of the invention.

FIGS. 3 a and 3 b are a cross sectional views of two additionalalternative designs for the natural draft low swirl burner of theinvention.

FIG. 4 illustrates the burner heat output and NOx output as a functionof exit velocity.

FIG. 5 illustrates flame position versus bulk velocity out of burner.

FIG. 6 illustrates the burner NOx output as a function of % excess air.

FIG. 7 illustrates the burner NOx output as a function of % excess airfor natural draft and forced draft conditions.

FIG. 8 illustrates a modified lower backpressure swirler according to anembodiment of the invention.

FIG. 9 illustrates that for a given fuel flow (heat output), themodified lower backpressure swirler provides higher air entrainment andhigher bulk velocity using the same venturi and fuel injection orifice.

FIG. 10 illustrates the dry NOx emissions of the LSB with the lowerbackpressure swirler as compared with the emissions of the LSB in theoriginal configuration.

FIG. 11 illustrates simulated dry NOx emissions, corrected to 3% oxygen,plotted against excess air.

FIG. 12 illustrates actual dry NOx emissions, corrected to 3% oxygen,plotted against excess air.

FIG. 13 illustrates actual dry NOx emissions for commercial and simpleventuris plotted against excess air.

FIG. 14 illustrates a modified natural draft slow swirl burner apparatusincluding a circular tube with a number of small holes placed around anexit cone according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention describe a novel burner-mixer apparatuswhich burns an ultra-lean premixed fuel-air mixture with a stable flamethat operates without a mechanical fan or blower to flow air through theburner apparatus. One embodiment of the invention utilizes fuel pressureto induce air flow though the burner assembly and achieve good mixing ofthe air and fuel prior to burning (hereafter referred to as a naturaldraft burner). An embodiment of the invention also establishes a weakswirl, or low swirl, on the fuel-air flow. The exit flow has a swirlnumber between about 0.01 and 3.0. The fuel pressure supplies the energyto create a well-mixed flow of air, fuel, and optionally, a diluent, toexit the system with adequate velocity and the exit flow has rotation ina plane normal to the axial flow. The flame burning in the exit regionperforms in the manner of a low swirl flame described in U.S. Pat. Nos.5,735,681 and 5,879,148 incorporated herein by reference as if fully setforth in their entirety.

The low swirl burner (LSB) is adaptable for a number of applications,including industrial heating, boilers, and gas turbines. In oneembodiment, the low swirl concept has been adapted to natural draftoperation, in which the fuel pressure, instead of an electricallypowered fan or blower, induces air flow through the burner. Naturaldraft burners are used at petroleum refineries and other sites whereflammable materials are processed to avoid the hazard of electric sparkgeneration.

Refineries currently use commercially available natural draft burners intheir process heaters, but are under pressure by regulatory agencies toreduce the emissions from their facilities, particularly for NOx. Thenatural draft burners currently available cannot satisfy upcomingemissions limits, so refineries may be faced with installation ofpost-combustion emission control strategies such as selective catalyticreduction (SCR). While SCR systems are capable of lowering NOxemissions, they have substantial installation and operating costs. Thesystems require careful monitoring to avoid release of ammonia, which isused in the NOx control chemistry.

The low swirl burner design offers ultra-low emissions as well as goodfuel flexibility and turndown. The low swirl design has been adapted tooperate in a natural draft configuration. In embodiments of theinvention, the burner and mixer components have been sized and orientedappropriately to provide good mixing, suitable air-fuel ratio, adequateLSB exit velocity, and a low swirl flow pattern.

Suitable LSB geometries were developed and testing was conducted.Emissions measurements demonstrated that the natural draft LSB hademissions that were equivalent to the standard LSB design that has beencommercialized. The petroleum industry anticipates that they will need aburner design that can provide less than 10 ppm NOx with 3% residualoxygen in the exhaust.

In premixed burner systems, NOx production increases with flametemperature and the fuel-air ratio. At fuel-air ratios that produce 3%oxygen in the exhaust, the flame temperature is sufficiently high suchthat more than 10 ppm NOx is produced. To avoid excessive NOxproduction, a diluent can be added to the fuel-air mix to reduce NOxproduction while maintaining low excess oxygen in the exhaust. Flue gasrecirculation (FGR) is an example of an effective NOx control strategyusing diluent addition.

Flue gas recirculation was incorporated into various embodiments of thenatural draft burner design by adding a flow path for the burner fluegas to the LSB mixer inlet. By adjusting the effective areas for air andflue gas into the LSB inlet, up to 30% flue gas recirculation may beachieved. The addition of FGR to the LSB design provided significant NOxreduction, and a range of conditions were identified that can satisfythe requirement of less than 10 ppm NOx at 3% oxygen in the exhaust.

In one embodiment, a natural draft low swirl burner has been developedthat is capable of achieving the NOx emissions requirements forrefineries. Additional embodiments address scale-up, performanceoptimization, fuel switching, and insuring stable operation at the fullrange of environmental conditions.

One application of an embodiment of the invention is for process heatingin petroleum refineries. For safety reasons, refineries use naturaldraft burners in their petroleum refining operations. The existingburners are capable of switching between operation with natural gas andwith hydrogen-containing refinery gas, but their NOx emissions exceedthe levels necessary to satisfy upcoming limits that are beingimplemented by air pollution control districts, particularly inCalifornia. The only currently-available method for refineries tosatisfy the emissions limits promulgated by air quality managementdistricts in California is to install post-combustion control systemssuch as selective catalytic reduction (SCR). SCR and similartechnologies have substantial installation, maintenance, and operatingcosts. The SCR system must be monitored carefully to avoid inadvertentrelease of ammonia.

Refineries would greatly prefer to install burners in their processheaters that would allow them to satisfy the new emissions requirements.If the natural draft adaptation of the low swirl burner iscommercialized and available for installation at refineries, it willallow them to process petroleum at a lower cost, and provide lower costproducts to consumers than the alternative of post-combustion emissioncontrol. Embodiments of the invention can be scaled up to a much largerheat output, and the components will be optimized for the operatingconditions found at refineries. Embodiments of the invention have beentested to insure that the design has adequate durability, reliability,and sufficient margin of safety over the entire range of potentialoperating conditions.

Besides refinery process heating, there are a number of otherapplications for the natural draft low swirl burner design. Oneembodiment of the invention has demonstrated that the natural draft LSBoperates well with vitiated (reduced oxygen content) air. Consequently,embodiments of the invention have significant potential for use in ductburner applications. Duct burners are used to heat air and exhauststreams for heat recovery steam generators, combined heat and powersystems, SCR reheating, and similar applications.

The natural draft low swirl burner design can also be applied to devicesthat currently use natural draft burners, either alone or with induceddraft exhaust. Potential applications include boilers, water heaters,and residential and commercial furnaces. Burners for some of theseappliances are relatively close in heat output to embodiments of theinvention and therefore should not be difficult to adapt the design tothese systems.

An embodiment of the low swirl burner (LSB) design is suitable fornatural draft operation with 30 psig gaseous fuel. The emissions,turndown, and flame stability of the LSB have been assessed with naturalgas and hydrogen-methane blends. The emissions have been compared withpredicted emissions levels for premixed flames.

Flue gas recirculation and fuel staging, techniques for emissionsreduction at low excess air, have been incorporated into the naturaldraft low swirl burner to demonstrate the capability of achievingsignificant emissions reductions at low excess air levels.

Embodiment 1 Demonstration of Natural Draft Operation with a Small ScaleLSB with at Least 3:1 Turndown Using the Following Fuels

methane

20% H₂/80% CH₄

42% H₂/58% CH₄

As discussed above, the low swirl burner is an innovative burner designfor premixed flames that utilizes a unique flame stabilization mechanism(Littlejohn and Cheng, 2007). The design has been commercialized forprocess heating by Maxon/Honeywell and is under development for gasturbines, as well as adaptation for residential and commercialappliances.

Referring to FIG. 1, burner apparatus 100 includes a venturi system 102attached to the inlet of a 2 inch (5 cm) diameter low swirl burner 104.The venturi 102 uses a 0.043 inch (0.11 cm) diameter fuel jet 106 toentrain air into the burner 100. Larger fuel jets were found to haveinsufficient air entrainment for good flame stability with 30 psigmethane. The venturi 102 has air inlets 108 on the side and bottom. Theair inlets 108 can be partially blocked to decrease the air/fuel ratio.The burner system 100 is also shown schematically in FIG. 2 a. Methaneand hydrogen are supplied by standard gas cylinders at 30 psig, and fuelflows are measured with rotameters and/or mass flow meters.

Emissions measurements were performed by enclosing the flame with aquartz cylinder (not shown) to prevent dilution of the exhaust gas withoutside air. A continuous gas sample was collected at the top of thequartz cylinder, cooled and dried and flowed through a Horiba PG250multi-gas analyzer. The analyzer measures NOx, CO, CO₂ and O₂. Theanalyzer was calibrated daily with calibration gases.

For measurements of turndown capability, methane flow to the venturiorifice was gradually increased until a stable flame could bemaintained. Emission measurements were recorded while the methane flowwas ramped up to the maximum flow possible with a 30 psig source. Thedata are compiled in Table 1 below. The fuel flow and the measuredoxygen concentration in the exhaust were used to calculate the bulk flowvelocity through the low swirl burner. The values of NOx in lb/MMBtuwere calculated using the following equation:

NOx=(1 MMBtu/flame Btu)*(air flow/hr)*(meas. NOx conc.)*(46 g/mole/454g/lb)

This calculation is based on molar volumes at 0° C. (32° F.), and givesslightly higher numbers than some of the equations used in regulatorydocuments that use 60° F. (15.6° C.) as the reference temperature. FIG.4 illustrates the burner 100 heat output (diamonds) and NOx output(circles) as a function of exit velocity. Even in a non-optimizedsystem, the LSB demonstrates over 4:1 turndown capability. The NOxemissions readings were multiplied by 10 to make the values comparableto the heat output. Similar behavior is observed when methane/hydrogenblends are used instead of methane alone. Some measurements wereobtained with the air inlet partially blocked so the system operated atlower excess air levels.

As can be seen in FIG. 4, NOx emissions increase more rapidly than thefuel flow to the burner. This is a result of less air entrainment athigher fuel flows due to the increasing backpressure of the burnersystem 100. As the air/fuel ratio of the burner decreases, the flametemperature, and NOx production, increase.

At high flow rates, the flow through the orifice transitions to chokedflow. Four times the volume of hydrogen is needed to consume the oxygenthat is consumed by burning a given volume of methane,

4H₂+2O₂=4H₂O

CH₄+2O₂=CO₂+2H₂O

and to obtain a fixed level of excess air, the volume of fuel increasesas the fraction of hydrogen in the fuel increases. The diameter of thefuel injection 106 orifice was fixed for these initial studies, and itwas difficult to obtain low excess air levels with 42% hydrogen-58%methane fuel blends since the higher volumetric flow created choked flowconditions at the orifice. As part of the burner optimization, a largerorifice may be used to assess LSB performance at low excess air and highhydrogen fuel content.

The Horiba analyzer uses a NDIR (non-dispersive infra-red) detectionsystem for carbon monoxide. This type of detector is subject tointerference from other gases in the exhaust system, which can result innegative signals when the CO concentration is low. A Bendix model 8501NDIR CO analyzer was used to confirm this observation. A report byJernigan et al (2002) from Thermo Environmental Instruments discussespotential interference in NDIR CO systems in more detail.

The flame stabilization mechanism of the low swirl burner 100 limits theminimum velocity at which the burner can operate. The flamestabilization is a result of the gas velocity downramp that occurs asthe gases flow out of the burner 100. The flame front settles to thelocation where the air/fuel velocity matches the flame speed. If thevelocity out of the burner is too low, the flame will propagate backinto the burner and attach to the swirler body 104. The swirler 104 willthen act as a mechanical flame holder, similar to conventional burnerdesigns. This is shown graphically in FIG. 5 which illustrates flameposition versus bulk velocity out of burner. U_(o) represents the bulkvelocity out of burner, and the flame position is the height above theburner exit. S_(L) represents laminar flame speed. Flame speed isdependent on the composition of the fuel. For example, hydrogen has ahigher flame speed than methane. As shown in the FIG. 5, a flame with ahigher flame speed will propagate into the burner at a higher exitvelocity than a flame with a lower flame speed.

This information may be utilized for designing a low swirl burner systemthat will have stable operation with all fuel types and fuel flows thatthe system will experience. Burner manufacturers prefer to build in asafety margin so the burners can tolerate off-normal conditions.

The performance of the LSB system used for these measurements has notbeen fully optimized, and significant performance gains are likely byreducing the burner backpressure and matching the fuel mixing venturi tothe LSB swirler. A computational fluid dynamics (CFD) analysis of theventuri-swirler assembly will assist in defining the important systemparameters.

Turndown studies were also done with approximately 20% hydrogen and 40%hydrogen in the fuel. The fuel measurement and control systems wereoperating near their lower limits at times, and it was difficult toobtain precise values of hydrogen content. The results are alsotabulated in Table 1. The performance with fuel blends was found to besimilar to methane-only flames shown in FIG. 4.

Embodiment 2 Obtaining Baseline NOx Emissions from the Same Burner inForced Draft Operation

Emissions measurements from the low swirl burner under forced draftconditions provide a good reference for understanding the performance ofthe burner under natural draft operation. The venturi 100 was removedfrom the LSB 100 (see for example FIG. 2 b and FIG. 3A), and the burnerwas attached to a flow system that supplies well-mixed air and fuel.Well-defined flows were established by feeding house compressed airthrough a turbine meter and methane through a mass flow controller. Whenhydrogen was included in the fuel blend, it was flowed through a massflowmeter and flow was controlled with a needle valve. The combined flowwas fed into the LSB, and the same arrangement was used to measure theburner emissions. The results are shown in FIG. 6, NOx data correlatedwell with a well-regarded study on NOx production in premixed combustionsystems from Leonard and Stegmaier (1994). The data is also compiled inTable 2 below.

As can be seen from the FIG. 6, the NOx emissions data measured hereagree well with the data from the Leonard-Stegmaier study. For fuelswithout significant fuel-bound nitrogen, NOx production in flames isclosely correlated with flame temperature, and flame temperatureincreases as excess air decreases. Thermal NOx production (Zeldovichmechanism) is the primary production process in flames with relativelylow excess air. The most straightforward method to reduce NOx incombustion exhaust gases is to operate with sufficient excess air tobring NOx within the necessary limits.

When operating with excess air is not practical (for example a highertemperature or higher efficiency is needed), techniques such as flue gasrecirculation (FGR) (see FIGS. 3 a and 3 b) or fuel staging can be usedto reduce emissions. These techniques are explored for use with thenatural draft low swirl burner.

The emissions observed with the forced draft and natural draft LSBtesting can be compared to assess the effectiveness of the venturi inmixing air and fuel. If the air and fuel are not well mixed, there willbe fuel-rich regions in the flame zone that will burn hotter than thebulk mixture and generate excess NOx. Similarly, fuel-poor regions willburn cooler and can incompletely burn the fuel, potentially leading tohigh levels of CO, formaldehyde, and unburned hydrocarbons.

The NOx emissions of the low swirl burner under forced draft operationand under natural draft operation are shown in FIG. 7. Within theaccuracy of the measurements, the NOx emissions of the two operatingmodes are the same. This indicates that the venturi is producing afairly uniform mixture of fuel and air, in spite of relatively simplefabrication from standard pipe fittings. The mixedness of the flow outof the venturi can be assessed by conducting a series of measurements ofthe fuel concentration to determine the variation in concentration.However, since the mixing is satisfactory, this is not necessary.

Another embodiment seeks to improve the performance of the natural draftburner by incorporating a commercially available venturi and testingswirlers with lower backpressures. Commercial venturis have beenoptimized for operation with natural draft burners. Swirler designs thathave been adapted to reduce backpressure should allow operation athigher bulk velocities, which should expand the range of stableoperation. This embodiment expands the operating range of the naturaldraft low swirl burner. Also, the improved LSB system is utilized forthe studies on flue gas recirculation and fuel staging described below.

Embodiment 3 Optimization of Natural Draft LSB to Improve Performance.Vary Injection and Premixing Configuration to Optimize Natural DraftBurner to Achieve the Same Emissions as Forced Draft LSB SwirlerOptimization

In the preceding, the low swirl burner under natural draft operationdemonstrated emissions that were comparable to those obtained underforced draft operation. The burner was close to the flashback limit atthe lowest range of exit velocities studied. To allow for at least 3:1turndown while maintaining a good safety margin to avoid flashback, itis desirable to operate at higher velocities than those described above.There is a limited amount of energy in the 30 psig fuel to entrain airand push it through the burner assembly, so an efficient venturipremixer and a low backpressure LSB are needed to optimize systemperformance.

A lower backpressure swirler for the LSB has been designed andfabricated. The new swirler has fewer vanes with a more aerodynamicprofile to provide less backpressure. An illustration of the lowerbackpressure swirler is shown in FIG. 8. The original swirler describedabove has 8 overlapping vanes and significantly more backpressure.

With the existing venturi used earlier, the new swirler allows operationat >6 m/s exit velocity, whereas the swirler used previously was limitedto <5 m/s. The new design offers at least 20% increase in flow rate, andthere is potential for additional improvement through a CFD(computational fluid dynamics) optimization of the flow systemcomponents. FIG. 9 illustrates that for a given fuel flow (heat output),the new swirler provides higher air entrainment and higher bulk velocityusing the same venturi and fuel injection orifice.

A screen or other flow restriction is used in the center section of theswirler to obtain the proper flow split between the non-swirling coreflow and the swirling annular flow. An equation has been developed todefine a swirl number based on the flows and geometry of the LSB(Johnson et al, 2005). A swirl number of ˜0.5 has found to work well formost applications. Several center screens were tested with the newswirler. Screens with little blockage reduce the LSB backpressure butcan result in unstable flames. A center screen with 32% open area wasfound to provide good flame stability and relatively low backpressure.The screen can be replaced with a tapered central body to reduce thepotential for flame attachment to the swirler.

In FIG. 10, the dry NOx emissions of the LSB with the new swirler arecompared with the emissions of the LSB in the original configuration.The new design shows the same emissions behavior as the original LSBsystem operated in natural draft mode. These emissions are consistentwith the values expected from burning well-mixed fuel and air. Data fromthe tests of the new swirler with methane and methane-hydrogen blendsare compiled in Table 3 below.

LSB-Venturi Optimization

Air entrainment in venturis has been studied for many years (von Elbeand Grumer, 1948) and commercial venturi designs incorporate theguidelines developed from these studies. A commercial burner venturi wasacquired and its performance with the low swirl burner is reportedbelow.

The optimum fuel injection orifice for the venturi will provide good airentrainment, good air/fuel mixing, and accommodate a range of fuelcompositions. A parametric study of fuel injection orifice sizes withthe existing venturi was performed. Fuel injection orifices with holesequivalent to #57, #53, and #52 drill sizes were tested. For a givenfuel flow rate, the smallest orifice generated the highest burner exitvelocity. However, the larger orifices allow operation at higher heatoutputs at a given fuel supply pressure. An excessively small orificewill limit the fuel flow to unacceptably low values, while anexcessively large orifice may not create adequate fuel/air mixing. Fuelinjectors with orifices in the range of #57 to #55 drill size providethe best performance in the current venturi-LSB configuration.

In fuel blends, the fuel heat content per unit volume varies. Forexample, natural gas has over three times the energy content of hydrogenon a volumetric basis. Therefore, to maintain steady heat input into aburner, it is necessary to modulate the fuel flow in conjunction withthe hydrogen content of the fuel. The fuel injection orifice must becapable of delivering a range of fuel flow rates in response to fuelcomposition and heating needs while supplying well-mixed air and fuel tothe burner.

Following simulated flue gas recirculation studies, the system wasadapted to utilize actual flue gas in the recirculation system. The goalis to reduce NOx emissions at low excess air conditions.

Embodiment 4 Conduct of Simulated FGR Studies with Natural Draft LSBSimulated FGR Studies

In the previous example, the emissions from the natural draft low swirlburner were assessed as a function of excess air. The NOx emissionsincreased as excess air was reduced, as would be expected from theincreasing flame temperatures associated with the richerstoichiometries. Flue gas recirculation (FGR) is often used inindustrial combustion systems to improve emissions (Baltasar et al,1997). FGR does not alter the oxygen concentration in the exhaust gassince it does not alter the air-fuel ratio in the flame zone.

The effect of simulated flue gas recirculation on LSB emissions wasstudied. To simulate FGR, a measured flow of nitrogen was fed into theventuri inlet feeding the low swirl burner. See FIGS. 3 a and 3 b. Thenitrogen, along with some of the air flowing into the inlet, creates ablend with an oxygen concentration that matches the oxygen concentrationin the exhaust gas. This is a simplification of a combustion systemusing FGR, since flue gas also contains carbon dioxide and water vapor.However, it can provide an indication of how FGR affects burneremissions. Measurements were made on the burner with simulated FGR flowsranging from zero to >40% FGR. Only methane was used as a fuel for thisseries of measurements. The simulated dry NOx emissions, corrected to 3%oxygen, are plotted against excess air in FIG. 11. The data are alsotabulated in Table 4 below. Some of the data in the FIG. 11 for the “noFGR” case are from measurements reported above.

The addition of FGR shifts the NOx vs. excess air curve to the left, sothat NOx at a given excess air value decreases as FGR increases. Thisdemonstrates that with sufficient FGR, single digit NOx levels can beobtained at low excess air.

Actual FGR Studies

While the data obtained with simulated flue gas recirculation indicatethat it is possible to operate a natural draft LSB with single digit NOxemissions at low excess air, the use of actual flue gas in theexperiments provides a more compelling case for the benefits of FGR.When FGR is used, it is desirable to avoid cooling the flue gas tomaintain high system efficiency. Feeding hot flue gas into the air-fuelblend will raise the flame temperature, which, in turn, can raise NOxlevels. Demonstration of NOx reduction with actual flue gasrecirculation makes a strong case for use of FGR to control NOx.

To explore the impact of actual FGR on LSB emissions, four 0.5 inchdiameter tubes were placed around the burner between the flame enclosureand the venturi inlet (See FIG. 3 a). The negative pressure created bythe venturi was sufficient to provide up to approximately 20% FGR.Nitrogen was also injected into the venturi inlet to access higherapparent levels of FGR. For this series of measurements, an all-metalswirler assembly was used that could tolerate the higher inlettemperatures associated with FGR.

The flow rate through the tubes to recirculate flue gas was estimatedfrom the fuel flow rates, the residual oxygen concentration, and theestimated total air entrainment rate by the venturi. Both methane andmethane-hydrogen blends were used as fuels for these measurements. Theactual dry NOx emissions (corrected to 3% O₂) as a function of excessair are shown in FIG. 12, and the data are compiled in Table 5 below.Due in part to the uncertainties with the flows in the system, there ismore scatter in the data. However, there is a clear trend that shows FGRshifts the NOx vs. excess air curve to the left. Again, single digit NOxlevels can be achieved at low excess air with sufficient flue gasrecirculation.

Embodiment 5 Testing of the LSB with a Commercial Venturi/Inspirator

A commercial venturi/inspirator sized for ˜100 kBtu/h burners wasobtained from Fives North American. It was coupled with the low swirlburner assemblies used in the earlier testing and operated over a rangeof conditions. The LSBs displayed good performance when fed by thecommercial venturi. Dry NOx emissions were comparable to those obtainedin the earlier experiments, as shown in FIG. 13. The red and bluesymbols represent earlier measurements obtained with the simple venturi,and the green symbols represent new data obtained with the commercialventuri. This also confirms that the simple venturi is achievingadequate air/fuel mixing. The data obtained with the commercial venturiare compiled in Table 6.

The commercial venturi has been optimized to entrain combustion air andachieve good mixing. This was demonstrated by the firing rates andburner exit velocities obtained in testing the low swirl burners. It waspossible to operate at 10% higher flow rates than those obtained withthe simple venturi system. This will translate into better turndowncapability and better flame stability. The commercial venturi alsoallows for finer adjustment of the air-fuel ratios by use of a threadedflange to control the air inlet gap width.

Assess Potential of FGR and Fuel Staging with Natural Draft LSB.

The use of flue gas recirculation (FGR) with the low swirl burner (LSB)operating in natural draft mode demonstrated that FGR has the potentialto maintain low NOx emissions at low excess air conditions. Anotherstrategy to control NOx emissions from combustion is fuel staging. Asystem with fuel staging uses a lean primary flame to limit initial NOxproduction. The remainder of the fuel is injected into the primary flameexhaust to consume some of the residual oxygen, and the exhaust from thesystem can have 3% oxygen or less. Since the secondary flame is burningvitiated (oxygen-depleted) air, it can have lower NOx emissions than ifit burned in non-vitiated air.

The fuel staging tests were conducted by injecting fuel into the base ofthe enclosure for the LSB flame. The same low swirl burner and venturithat were used in the earlier measurements were incorporated into thetest system. Several configurations were tried for injection of thesecondary fuel. Generally, a circular tube with a number of small holeswas placed around the exit cone of the low swirl burner. A cross-sectionof the system is shown schematically in FIG. 14.

It was found that the secondary fuel injection holes tended to producediscrete yellow-tipped flames. The flame appearance indicated that thesecondary fuel was not mixing well with the exhaust gas from the primaryflame zone. To improve mixing, nitrogen was added to the secondary fuelflow to produce a ˜1:1 mixture of methane and nitrogen. The largervolume of gas should increase the jet velocity, and the nitrogen shouldslightly impede the onset of combustion. The position of the secondaryfuel injection ring was also moved to various heights above the base ofthe enclosure.

None of these variations had a significant effect on the appearance ofthe flames in the secondary combustion zone. Similarly, the measured NOxemissions were no better than that obtained by injecting all of the fuelinto the LSB. With higher secondary fuel flows, the NOx emissions may beslightly higher than equivalent flames without fuel staging.

To improve the dispersion of the secondary fuel injection, a very finestainless steel mesh was placed over the secondary fuel injection tube.The mesh was clamped down at the edges. The mesh dispersed the secondaryfuel flow into the exhaust gas over an extended area, and prevented thecreation of fuel jets in the exhaust gas. The flame generated by thecombustion of the secondary fuel was now more evenly dispersed. However,the NOx emissions were no better than those from equivalent flames inwhich all fuel was fed to the low swirl burner. Nitrogen was also addedto the secondary fuel flow in some tests to improve dilution and mixing.Again, there was no reduction in NOx levels. The fuel staging testresults are compiled in Table 7 below.

The lack of reduction in NOx levels with the addition of secondary fuelsuggests that there is inadequate mixing in the secondary fuel injectionzone. From our studies of the low swirl burner, we have found thatturbulence levels are not very high beyond the primary flame zone.Without rapid mixing of the secondary fuel with the exhaust gas, thesecondary combustion zone will not be well mixed, and NOx emissions willbe high. Fuel staging may be more effective at higher burner velocities.However, it will be difficult to achieve sufficiently high velocitieswith a natural draft low swirl burner for staged combustion.Alternatively, a very highly dispersed secondary fuel injection systemmay demonstrate better emissions performance.

Another approach for staged combustion is to create a rich(oxygen-deficient) primary combustion zone, and then blend in air toachieve the desired overall stoichiometry. Such burner systems aresometimes called RQL burners, for Rich-Quench-Lean combustion, orRich-Quick mix-Lean combustion. The rich primary zone has a relativelylow flame temperature and consequently does not produce high NOx levels.The rich primary zone can produce high levels of CO and unburnedhydrocarbons since there is not sufficient oxygen for completecombustion. The addition of secondary air lowers the overallstoichiometry to the desired level of excess air. One of the problemswith RQL burners is the combustion gas passes through stoichiometricconditions as the secondary air is added, and significant NOx productioncan occur at that point. Also, there can be issues with adequate burnoutof CO and unburned hydrocarbons after the secondary air addition. Thisversion of fuel staging is not likely to provide sufficient emissionsreduction with the low swirl burner for refinery conditions due to thelow excess air levels in the refinery system exhaust. Also, a powersource would be needed to supply the secondary air to the burnerassembly since the fuel is only inducing the flow of the primary air.

While it may be possible to develop a suitable fuel staging arrangementfor a natural draft low swirl burner, it is likely to requiresignificant development to create a satisfactory fuel injection andmixing system for the secondary fuel. Methane-hydrogen fuel blends havehigher flame speeds than methane alone and it will be more difficult toestablish a fuel staging system for these blends that providessignificant emissions reduction.

Embodiments of the invention demonstrate that FGR appears to besignificantly more promising than fuel staging for controlling NOxemissions. The flue gas recirculation system can be built into thenatural draft low swirl burner assembly to minimize heat loss and toutilize the induced draft from the fuel injection. With the low backpressure associated with the low swirl burner, a 30 psig fuel stream hassufficient energy to entrain both combustion air and flue gas, and thesystem will be capable of achieving low emissions and good turndown.

Turndown Capabilities of the Low Swirl Burner with FGR

Due to the limitations of the current test system used to recirculateflue gas, there was limited firing rate turndown capability when realFGR was used. The relatively small flow path for flue gas recirculationresulted in low FGR at low firing rates where there was small pressuredifferential between the burner inlet and the combustion chamber.Measurements were conducted over a 2:1 firing rate range. Over thisrange, the firing rate did not appear to have any significant influenceon emissions. Results from this study indicated that the two factorsthat significantly influenced emissions were excess air level and thefraction of FGR.

The natural draft LSB that did not incorporate FGR demonstrated ˜10:1turndown, so should be feasible to expand the turndown range with FGR.Adding FGR to a natural draft LSB is a matter of incorporating asuitable flow path for flue gas to be entrained into the burner inletwith the combustion air. Dampers with low actuation force can beincorporated into the inlet air and flue gas flows to control the FGRrate.

The low swirl burner, integrated with a suitable venturi, works well innatural draft configuration when fuel is available at ˜30 psig. For bestperformance, a low pressure drop swirler should be matched with thedesigned flow output of the venturi. The emissions of the natural draftlow swirl burner agree well with the emissions predicted by Leonard andStegmaier (1994). The natural draft LSB works well with both natural gasand natural gas-hydrogen blends.

NOx emissions increase as the system excess air is reduced and flametemperature increases. It is desirable to operate refinery processheaters at low excess air conditions to improve efficiency. Techniquessuch as flue gas recirculation (FGR) or fuel staging can lower NOxemissions from burners operating at low excess air conditions. Thenatural draft low swirl burner was operated with simulated and actualFGR and with fuel staging. The LSB with fuel staging did not show anyimprovement in NOx emissions over the unstaged natural draft LSB.However, tests with simulated and actual flue gas recirculationindicated that the low swirl burner can achieve single digit NOx levelsat low excess air when 20-30% FGR is utilized.

Embodiments of the invention demonstrate that the natural draft lowswirl burner has the capability to achieve low emissions at low excessair conditions, and are adaptable to a commercial product for processheating.

The foregoing detailed description of the present invention is providedfor purposes of illustration and is not intended to be exhaustive or tolimit the invention to the embodiments disclosed.

TABLE 1 Natural draft operation of test LSB with emissions measurements(including turndown). NOx, NOx, CO, CO₂, bulk fraction heat, excess ppmNOx, ppm ppm % O₂, % flow, m/s H₂ kBtu/h air @ 3% O₂ lb/MMBtu 1.3 386.43 9.78 1.49 0 19.9 79 2.1 0.0030 2.2 −11 6.89 8.92 2.02 0 29 67 3.30.0047 3.8 −14 7.44 7.85 3.01 0 47.2 54 5.2 0.0075 5.7 −13 7.82 7.14 3.70 61.1 47 7.4 0.0106 10.5 −10 8.29 6.23 5.07 0 89.2 38 12.8 0.0183 10022 10.26 2.15 3.96 0 89.2 11 95.5 0.1367 71 16 10.2 2.7 3.28 0 71.6 1469.8 0.1000 68 20 10 3.03 2.85 0 61.1 16 68.1 0.0975 16 −11 8.32 5.562.49 0.2 46.8 33 18.7 0.0262 18 −8 8.09 5.55 2.72 0.4 52.6 33 21 0.02863.4 −11 7.01 8.32 3.32 0.4 52.6 59 4.8 0.0066 3.5 −11 6.8 8.33 3.04 0.246.8 60 5 0.0070 2.4 −12 6.21 9.35 4.65 0.18 65.7 73 3.7 0.0052 2.6 −106.63 9 4.76 0.36 71.1 68 3.9 0.0054 0.2 >500 3.74 11.7 1.32 0.37 15.2111 0.4 0.0005 0.8 55 4.44 11.49 2.14 0.68 27.3 107 1.5 0.0019 0.9 5.94.35 11.38 2.46 0.76 32.6 105 1.7 0.0021 1.3 −6 4.83 10.59 3.1 0.77 44.691 2.3 0.0028 1.7 −7 5.11 10.07 3.78 0.78 57.4 83 2.8 0.0034 1.6 −105.77 9.91 2.37 0.44 33.2 81 2.6 0.0035 0.6 20 5.17 11 1.52 0.42 19 981.1 0.0015 0.2 >500 4.52 11.91 1.33 0.34 15 115 0.4 0.0005 2.7 −2 6.388.93 3.19 0.41 48.3 67 4 0.0055 3.2 −8 6.56 8.62 3.66 0.36 56.3 63 4.70.0064 3.8 −9 6.82 8.13 4.07 0.39 65.3 57 5.3 0.0073 4 −11 6.83 8.144.38 0.37 70.1 57 5.6 0.0077 0.2 >500 4.42 12.13 1.27 0.27 13.7 120 0.40.0006 0.2 >500 3.24 12.1 1.22 0.27 13.3 119 0.4 0.0006

TABLE 2 Forced draft operation of test LSB with emissions measurements.NOx, NOx, CO, CO₂, bulk fraction heat, excess ppm @ NOx, ppm ppm % O₂, %flow, m/s H₂ kBtu/h air 3% O₂ lb/MMBtu 2.5 −9 7.02 8.62 4.93 0 78.6 633.6 0.0048 5.9 −6 7.72 7.27 4.95 0 85.2 48 7.7 0.0105 10.9 3 8.3 6.24.97 0 91.7 38 13.3 0.0180 19.4 12 8.87 5.13 5 0 98.3 29 22 0.0298 2.2−8 6.86 8.82 4.91 0 74.7 66 3.3 0.0045 1.8 −10 6.65 9.2 4.9 0 72.1 712.8 0.0038 1.0 >500 6.09 9.71 4.89 0 68.1 78 1.6 0.0022 0.7 >500 5.5710.32 4.92 0.24 63.9 87 1.2 0.0017 1.9 −2 6.28 9.43 4.94 0.24 70.3 74 30.0041 3.4 −7 6.81 8.43 4.97 0.24 76.7 61 4.9 0.0067 6.2 −2 7.37 7.35 50.24 83.1 49 8.2 0.0113 10.7 6 7.87 6.35 5.03 0.24 89.5 39 13.2 0.018118.5 15 8.45 5.24 5.06 0.24 95.9 30 21.1 0.0291 0.3 >500 3.3 11.41 4.880.41 48 106 0.6 0.0009 0.9 3 4.99 11.16 4.91 0.41 54 101 1.7 0.0025 1.58 5.45 10.21 4.94 0.41 60 85 2.5 0.0038 2.8 1 5.95 9.22 4.97 0.41 66 714.3 0.0064 4.4 −2 6.41 8.24 5 0.41 72 58 6.2 0.0092 7.7 1 6.9 7.25 5.030.41 78 48 10.1 0.0149 13.2 5 7.36 6.25 5.06 0.41 84 38 16.1 0.0237 24.49 7.84 5.23 5.1 0.41 90 30 27.9 0.0410 3.6 7.6 7.01 8.71 2.92 0 48.7 645.3 0.0066 31 −4 9.1 4.89 2.98 0 63.8 28 34.7 0.0434 4.4 −11 7.34 8.073.67 0 63.8 57 6.1 0.0077 13 −9 8.43 6.12 3.75 0 74.6 37 15.7 0.0197 3.8−11 7.25 8.23 4.29 0 74.6 58 5.4 0.0067 0.8 17 5.27 10.95 4.22 0.41 62.498 1.4 0.0016 1.6 0.7 5.85 9.94 4.24 0.4 66.5 81 2.6 0.0031 3.6 −7 6.558.51 4.29 0.41 76.2 62 5.2 0.0060 8.6 −10 7.28 6.97 4.35 0.44 85.6 4511.1 0.0128 21.2 −5 7.96 5.54 4.44 0.46 92.8 33 24.7 0.0293 46 12 8.584.3 4.47 0.45 100.1 24 49.6 0.0590 12 −6 8.43 6.14 4.23 0 79.5 37 14.60.0194 21 −11 8.73 5.53 4.21 0 84.1 32 24.5 0.0318 44 −5 9.33 4.37 4.230 89.8 24 47.6 0.0623 82 16 9.86 3.29 4.25 0 95.2 17 83.4 0.1095 137 3610.42 2.28 4.27 0 100.6 12 131.7 0.1732

TABLE 3 Natural draft operation of LSBs: emissions and operatingconditions. NOx orifice NOx, CO, CO2, CH₄, H₂, U, frac excess @ NOx,size ppm ppm % O2, % lpm lpm m/s H2 kBtu/h air 3% O₂ lb/MMBtu runs withmethane 57 1.8 0.1 6.78 9.1 19.29 0 2.89 0 40.9 69 2.7 0.0039 57 2.8 −107.18 8.39 19.12 0 2.7 0 40.5 60 4 0.0057 57 17 −3 8.83 5.34 19.12 0 2.170 40.5 31 19.6 0.028 57 2.7 28 6.95 8.73 27.12 0 3.94 0 57.5 64 4 0.005757 2.8 28 7.06 8.63 27.12 0 3.9 0 57.5 63 4.1 0.0058 57 4.6 −6 7.65 7.5440.19 0 5.31 0 85.2 51 6.2 0.0088 57 5 −3 7.65 7.54 40.4 0 5.34 0 85.751 6.7 0.0096 57 4 −6 7.41 7.96 27.12 0 3.7 0 57.5 55 5.5 0.0079 57 4.1−6 7.37 8.04 27.12 0 3.73 0 57.5 56 5.7 0.0082 57 7.6 −7 8.15 6.63 40.190 4.98 0 85.2 42 9.5 0.0136 57 7.2 −9 8 6.89 40.4 0 5.09 0 85.7 44 9.20.0132 57 28 2.1 9.2 4.64 27.31 0 2.97 0 57.9 26 30.8 0.0441 57 25 29.13 4.82 27.31 0 3 0 57.9 27 27.8 0.0398 57 59 12 9.82 3.56 40.19 04.09 0 85.2 19 60.9 0.0872 57 43 11 9.88 3.43 40.4 0 4.09 0 85.7 18 44.10.0631 57 7 −6 8.19 6.5 46.37 0 5.69 0 98.3 41 8.7 0.0125 57 7.7 −7 7.857.16 46.37 0 5.96 0 98.3 47 10 0.0144 57 7 −7 7.9 7.05 46.37 0 5.91 098.3 46 9 0.013 53 9.4 −10 8.32 6.42 16.97 0 2.07 0 36 40 11.6 0.0166 5310 −10 8.42 6.2 16.97 0 2.04 0 36 38 12.2 0.0174 53 11 −12 8.31 6.3619.29 0 2.34 0 40.9 39 13.5 0.0194 53 9 −11 8.27 6.45 19.29 0 2.36 040.9 40 11.1 0.016 53 14 −12 8.63 5.64 24 0 2.78 0 50.9 33 16.4 0.023553 18 −9 8.8 5.45 24 0 2.74 0 50.9 32 20.9 0.0299 53 15 −11 8.89 5.2427.31 0 3.08 0 57.9 30 17.1 0.0245 53 19 −10 8.69 5.67 27.31 0 3.17 057.9 34 22.3 0.032 53 42 −2 9.5 4.18 56.27 0 5.95 0 119.3 23 45 0.064453 36 −2 9.33 4.48 56.27 0 6.05 0 119.3 25 39.2 0.0562 52 20 −6 8.8 5.5421.87 0 2.52 0 46.4 33 23.3 0.0334 52 19 −6 8.85 5.45 21.87 0 2.5 0 46.432 22 0.0315 52 31 −1 9.21 4.74 27.12 0 2.96 0 57.5 27 34.3 0.0492 52 28−1 9.39 4.41 27.12 0 2.91 0 57.5 24 30.4 0.0435 52 41 3 9.7 3.85 40.4 04.19 0 85.7 21 43 0.0616 52 53 7 9.91 3.47 40.83 0 4.14 0 86.6 18 54.40.0779 52 90 18 10.31 2.72 70.09 0 6.81 0 148.6 14 88.6 0.1269 52 83 1910.5 2.5 70.09 0 6.73 0 148.6 13 80.7 0.1156 52 105 34 10.5 2.53 70.09 06.74 0 148.6 13 102.3 0.1465 53 11.3 −1 8.38 6.2 52.88 0 6.36 0 112.1 3813.8 0.0197 53 12.1 −1 8.43 6.04 52.88 0 6.29 0 112.1 37 14.6 0.0209 5316.2 2.3 8.75 5.43 53.12 0 6.07 0 112.6 32 18.7 0.0268 53 19 2.2 8.85.33 53.12 0 6.03 0 112.6 31 21.8 0.0313 53 11.2 −6 8.32 6.23 28.25 03.4 0 59.9 38 13.7 0.0196 53 11.1 −7 8.25 6.19 28.25 0 3.39 0 59.9 3813.5 0.0193 53 6.8 −9 7.9 7.03 28.25 0 3.6 0 59.9 46 8.8 0.0126 53 5.1−13 7.57 7.63 17.96 0 2.39 0 38.1 52 6.9 0.0098 53 4.9 −13 7.59 7.5817.96 0 2.38 0 38.1 51 6.6 0.0094 53 3.9 −14 7.32 8.1 13.8 0 1.91 0 29.357 5.5 0.0078 53 3.7 −14 7.31 8.15 13.8 0 1.91 0 29.3 57 5.2 0.0074 532.5 −13 7 8.7 10.95 0 1.59 0 23.2 64 3.7 0.0053 53 2.6 −14 6.96 8.7710.95 0 1.6 0 23.2 65 3.8 0.0055 53 1.8 −13 6.62 9.26 8.81 0 1.34 0 18.771 2.8 0.004 53 1.6 −11 6.63 9.39 8.81 0 1.35 0 18.7 73 2.5 0.0036 530.9 22 6.13 10.32 6.9 0 1.15 0 14.6 87 1.5 0.0022 53 1 14 6.11 10.38 6.90 1.16 0 14.6 88 1.7 0.0024 53 1.4 −10 6.5 9.68 6.9 0 1.09 0 14.6 77 2.20.0032 53 1.4 −5 6.44 9.75 6.9 0 1.09 0 14.6 78 2.2 0.0032 57 3.1 −97.21 8.47 35.36 0 5.04 0 75.2 61 4.5 0.0064 57 3.3 −9 7.19 8.51 35.36 05.05 0 75.2 62 4.8 0.0068 runs with methane-hydrogen blends 53 1.7 −95.55 10.02 9.09 10.01 1.88 0.52 26.5 82 2.8 0.0037 53 1.8 −10 5.62 9.879.09 10.01 1.86 0.52 26.5 80 2.9 0.0039 53 2.1 −11 5.62 9.73 11.69 14.962.44 0.56 35.6 78 3.4 0.0044 53 2 −11 5.58 9.8 11.69 14.96 2.46 0.5635.6 79 3.2 0.0042 53 2.7 −11 5.9 9.36 13.34 14.59 2.6 0.52 38.8 73 4.20.0056 53 2.7 −11 5.88 9.34 13.34 14.59 2.6 0.52 38.8 73 4.2 0.0056 532.1 −11 5.71 9.53 13.34 17.17 2.74 0.56 40.7 75 3.3 0.0044 53 2.3 −125.69 9.57 13.34 17.17 2.75 0.56 40.7 76 3.6 0.0048 53 2 −10 5.42 9.8113.34 21.46 2.98 0.62 43.8 79 3.2 0.0042 53 2.1 −10 5.48 9.67 13.3421.46 2.94 0.62 43.8 77 3.3 0.0043 53 2.8 −11 5.86 9.26 16.97 21.11 3.380.55 51.2 71 4.3 0.0057 53 2.5 −11 5.87 9.23 16.97 21.11 3.37 0.55 51.271 3.8 0.0051 53 3.5 −11 6.35 8.58 21 20.05 3.73 0.49 59 63 5.1 0.006853 3.3 −12 6.23 8.8 21 20.05 3.8 0.49 59 65 4.9 0.0065 53 4 −11 6.678.15 26.74 20.05 4.4 0.43 71.2 57 5.6 0.0076 53 4.4 −10 6.69 8.12 26.7420.05 4.39 0.43 71.2 57 6.2 0.0083 53 5.1 −12 6.72 8.03 26.93 20.05 4.390.43 71.6 56 7.1 0.0096 53 4.6 −10 6.68 8.12 26.93 20.05 4.42 0.43 71.657 6.4 0.0087 53 10.6 −9 7.4 6.65 26.93 20.05 3.96 0.43 71.6 42 13.30.018 53 9.6 −10 7.44 6.5 26.93 20.05 3.92 0.43 71.6 41 11.9 0.0162 5316.4 −6 7.93 5.94 34.13 17.17 4.54 0.33 84.7 36 19.6 0.027 53 12.7 −77.99 5.84 34.13 17.17 4.51 0.33 84.7 35 15.1 0.0208 53 20 −2 8.22 5.5239.97 17.54 5.1 0.3 97.4 32 23.3 0.0322 53 17.8 −4 8.19 5.56 39.97 17.545.11 0.3 97.4 33 20.8 0.0287 53 7.7 −7 7.43 7.07 39.97 17.54 5.67 0.397.4 46 10 0.0138 53 7 −6 7.42 7.09 39.97 17.17 5.66 0.3 97.1 46 9.10.0126 53 8 −5 7.39 6.97 43.46 23.19 6.25 0.35 108.9 45 10.3 0.0141 538.2 −6 7.42 6.95 43.46 23.19 6.24 0.35 108.9 45 10.5 0.0144 57 1.7 −46.36 9.4 25.08 8.45 4.18 0.25 59.3 73 2.6 0.0037 57 3.1 0 6.56 8.9821.69 6.86 3.47 0.24 50.9 68 4.7 0.0065 57 3.8 −8 6.86 8.45 27.12 7.464.11 0.22 62.9 61 5.5 0.0076 57 4.5 −9 7.15 8.12 32.13 5.66 4.64 0.1572.2 57 6.3 0.0089 57 4.9 −10 7.2 8.08 32.13 5.66 4.62 0.15 72.2 57 6.80.0096 57 2.9 −8 6.81 8.86 32.53 4.85 4.95 0.13 72.5 66 4.3 0.0061 57 3−9 6.84 8.77 32.53 4.85 4.91 0.13 72.5 65 4.4 0.0063 57 2.5 −8 6.38 9.3430.36 13.08 5.14 0.3 73.8 73 3.9 0.0054 57 2.6 −5 6.42 9.26 30.36 13.085.1 0.3 73.8 71 4 0.0055 57 2.6 −10 6.17 9.56 29.2 17.72 5.24 0.38 74.776 4.1 0.0056 57 2.4 −10 6.22 9.45 29.2 17.72 5.19 0.38 74.7 74 3.80.0051 57 2.1 −10 6.15 9.57 28.25 20.93 5.22 0.43 75 76 3.3 0.0045 572.2 −8 6.04 9.64 28.25 20.93 5.25 0.43 75 77 3.5 0.0047

TABLE 4 Effect of simulated flue gas recirculation on NOx emissions froma natural draft LSB fraction NOx, CO, CO2, CH4, H2, U, fraction excessNOx @ lb NOx/ FGR ppm ppm % O2, % lpm lpm m/sec H2 kBtu/h air, % 3% O2MMBtu 0.01 2.4 2 6.98 8.6 29.01 0 4.19 0 61.5 63.1 3.5 0.005 0.36 2.6 336.6 4.52 29.01 0 3.97 0 61.5 25.2 2.8 0.0041 0.17 3.1 3 6.93 6.33 29.010 3.91 0 61.5 39.2 3.8 0.0055 0.01 2.8 −7 7.08 8.44 29.01 0 4.13 0 61.561.1 4 0.0058 0.01 3.2 −6 7.15 8.33 36.39 0 5.13 0 77.1 59.8 4.6 0.00650.13 3.6 −8 7.18 6.24 36.39 0 4.78 0 77.1 38.4 4.4 0.0063 0.29 3 −6 6.864.63 36.39 0 4.79 0 77.1 25.9 3.3 0.0047 0.01 6.1 −10 7.73 7.22 27.68 03.59 0 58.7 47.6 8 0.0114 0.18 7.9 −6 7.68 4.52 27.68 0 3.38 0 58.7 25.28.6 0.0124 0.38 7 −1 7.29 2.46 27.68 0 3.49 0 58.7 12.7 6.8 0.0097 0.367.2 −3 7.24 2.78 29.01 0 3.67 0 61.5 14.5 7.1 0.0102 0.31 7 −6 7.41 3.229.01 0 3.6 0 61.5 16.9 7.1 0.0101 0.17 7.4 −7 7.62 4.58 29.01 0 3.53 061.5 25.6 8.1 0.0116 0.01 6.8 −9 7.8 6.91 29.01 0 3.68 0 61.5 44.5 8.70.0125 0 7.1 −11 7.92 6.86 20.48 0 2.58 0 43.4 44.1 9.1 0.013 0 7.5 −127.79 7.1 20.48 0 2.62 0 43.4 46.4 9.7 0.0139 0.24 6.8 −9 7.47 4.12 20.480 2.55 0 43.4 22.5 7.3 0.0104 0.38 5.6 −7 7.05 2.76 20.48 0 2.62 0 43.414.4 5.5 0.0079 0.19 7.3 −9 7.6 4.34 26 0 3.17 0 55.1 24 7.9 0.0113 0.46.4 −5 7.15 2.43 26.19 0 3.35 0 55.5 12.5 6.2 0.0089 0.58 5.3 390 6.511.47 26.37 0 3.62 0 55.9 7.5 4.9 0.007 0.31 7.9 2 7.55 2.4 34.13 0 4.1 072.4 12.4 7.6 0.0109 0.45 6.7 24 7.09 1.5 34.34 0 4.35 0 72.8 7.6 6.20.0088 0.15 9 −5 7.87 4.11 33.73 0 3.94 0 71.5 22.5 9.6 0.0137 0 3.5 107.09 8.48 24.36 0 3.46 0 51.6 61.6 5 0.0072 0.06 4 2 7.19 7.62 24.54 03.37 0 52 51.8 5.4 0.0077 0.12 4.2 3 7.14 6.75 24.63 0 3.32 0 52.2 435.3 0.0076 0.24 4.3 13 7.02 5.36 24.63 0 3.27 0 52.2 31.2 5 0.0071 0.363.7 13 6.87 4.22 24.63 0 3.31 0 52.2 23.2 4 0.0057 0 3.8 14 7.1 8.5324.54 0 3.5 0 52 62.2 5.5 0.0079 0.05 4.3 8 7.19 7.61 24.72 0 3.39 052.4 51.6 5.8 0.0083 0.12 4.2 −1 7.2 6.64 24.81 0 3.31 0 52.6 42 5.30.0075 0.24 4.2 11 7.03 5.39 24.9 0 3.31 0 52.8 31.5 4.8 0.0069 0.2410.8 −11 7.81 3.57 24.9 0 3.01 0 52.8 19.1 11.2 0.016 0.35 9.5 −3 7.492.66 24.72 0 3.09 0 52.4 13.8 9.3 0.0133 0.26 13.1 −3 8.02 2.5 33.33 03.9 0 70.7 12.9 12.7 0.0182 0.18 14.3 −4 8.28 3.28 33.33 0 3.81 0 70.717.3 14.5 0.0208 0.09 16 −10 8.46 4.4 33.33 0 3.81 0 70.7 24.4 17.40.0248 0.09 6.1 −11 7.58 6.14 33.13 0 4.2 0 70.2 37.5 7.4 0.0106 0.186.2 −10 7.52 4.91 33.33 0 4.15 0 70.7 27.9 6.9 0.0099 0.26 5.7 −6 7.344.12 33.13 0 4.19 0 70.2 22.5 6.1 0.0087 0.05 5.8 −13 7.67 6.71 32.93 04.22 0 69.8 42.6 7.3 0.0105 0 5.7 −12 7.66 7.42 32.73 0 4.29 0 69.4 49.67.6 0.0108 0 3.9 −10 7.26 8.17 25.27 0 3.51 0 53.6 57.9 5.5 0.0079 0.064.2 −9 7.34 7.23 25.54 0 3.42 0 54.2 47.7 5.5 0.0079 0.12 4.5 −9 7.286.42 25.45 0 3.35 0 54 40 5.6 0.008 0.23 4.4 −5 7.16 5.11 25.45 0 3.32 054 29.3 5 0.0071 0.34 3.9 1 6.93 4.15 25.54 0 3.39 0 54.2 22.7 4.2 0.0060.25 5.7 0 6.93 4.15 25.45 0 3.18 0 54 22.7 6.1 0.0087 0.16 6.5 −4 7.524.45 25.45 0 3.07 0 54 24.7 7.1 0.0101 0.12 6.7 −7 7.63 5.65 24.9 0 3.120 52.8 33.5 7.9 0.0101 0.24 6.6 −3 7.45 4.35 24.9 0 3.13 0 52.8 24 7.10.0101 0.35 5.7 0 7.21 3.33 24.9 0 3.2 0 52.8 17.6 5.8 0.0101 0.42 5 56.98 2.9 25.08 0 3.31 0 53.2 15.2 5 0.0101

TABLE 5 Effect of flue gas recirculation on LSB NOx emissions fractionNOx, CO, CO2, CH4, H2, U, fraction excess NOx @ lb NOx/ FGR ppm ppm %O2, % lpm lpm m/sec H2 kBtu/h air, % 3% O2 MMBtu 0 8.3 −11 8.17 6.5724.2 0 2.98 0 51.3 41.3 10.4 0.0149 0 9.5 −11 8.21 6.49 32.3 0 3.97 068.5 40.6 11.8 0.0169 0.05 8.8 −9 8.58 5.83 24.2 0 2.84 0 51.3 34.9 10.50.015 0.09 12.1 −3 8.8 5.43 32.3 0 3.7 0 68.5 31.8 14 0.0201 0.11 12 −139.42 4.85 24.2 0 2.66 0 51.3 27.5 13.4 0.0192 0 8.8 −12 8.02 6.97 24.2 02.89 0 51.3 45.1 11.3 0.0152 0.06 8.3 −11 7.93 6.13 24.2 0 2.92 0 51.337.5 10.1 0.0145 0.12 7.8 −11 7.91 5.15 24.2 0 2.93 0 51.3 29.6 8.90.0137 0.2 7 −10 7.63 4.01 24.2 0 3.03 0 51.3 21.8 7.4 0.0127 0.28 6.5−7 7.26 3.23 24.2 0 3.18 0 51.3 17.1 6.6 0.0124 0 8.1 −11 8.41 6.13 24.20 2.76 0 51.3 37.5 9.8 0.0134 0.1 8.6 −10 8.41 5.19 24.2 0 2.76 0 51.329.9 9.8 0.0143 0.16 8.8 −9 8.29 4.3 24.2 0 2.8 0 51.3 23.7 9.5 0.01480.24 9.1 −8 8.03 3.02 24.2 0 2.89 0 51.3 15.8 9.1 0.0157 0.32 8.9 −27.73 2.04 24.2 0 3 0 51.3 10.5 8.4 0.016 0.01 7.6 −11 7.27 7.61 24 3.513.35 0.13 53.41 51.5 10.2 0.0155 0.01 5.8 −10 6.87 7.99 24 9.62 3.720.29 57.82 55.6 8 0.0122 0.05 6.5 −10 7.05 6.72 24 9.62 3.5 0.29 57.8242.6 8.2 0.0128 0.1 6.2 −10 6.71 6.16 24 9.62 3.51 0.29 57.82 37.6 7.50.0123 0.17 6.1 −9 6.56 4.62 24 9.43 3.45 0.28 57.68 25.8 6.7 0.01190.17 4.6 −10 6.07 5.62 24 15.81 3.85 0.4 62.28 33.1 5.4 0.0093 0.09 4.6−10 6.46 6.5 24 15.85 3.81 0.4 62.31 40.6 5.7 0.0092 0.06 4.5 −10 6.57 724 15.78 3.84 0.4 62.26 45.2 5.8 0.009 0.01 6 −9 6.79 7.77 24 15.78 3.90.4 62.26 53.2 8.2 0.0123 0 6 −11 7.19 7.7 24 3.59 3.39 0.13 53.47 52.48.1 0.0124 0 5.5 −12 7.15 7.41 24 9.7 3.56 0.29 57.88 49.4 7.3 0.0110.05 6.9 −11 7.07 6.43 24 9.62 3.45 0.29 57.82 39.9 8.5 0.0134 0.04 6−11 6.97 6.59 24 9.59 3.48 0.29 57.79 41.4 7.5 0.0118 0.09 7.3 −11 7.125.22 24 9.59 3.33 0.29 57.79 30.1 8.3 0.0137 0.16 5.5 −11 6.66 4.12 249.62 3.37 0.29 57.82 22.5 5.9 0.0105 0.16 5.4 −10 6.49 4.33 24 15.813.61 0.4 62.28 23.8 5.8 0.0102 0.08 4.9 −10 6.73 5.69 24 15.81 3.63 0.462.28 33.7 5.8 0.0093 0.04 4.7 −10 6.73 6.73 24 15.7 3.75 0.4 62.2 42.75.9 0.0092 0 5.5 −12 6.96 7.38 24 15.7 3.79 0.4 62.2 49 7.3 0.0109 0.046.9 −10 7.75 6.65 24 3.51 3.16 0.13 53.41 41.9 8.7 0.0133 0.04 6.2 −127.56 6.6 24 9.74 3.38 0.29 57.91 41.5 7.8 0.0118 0.09 7.7 −12 7.76 4.9624 9.74 3.17 0.29 57.91 28.2 8.6 0.0138 0.13 9.4 −9 7.87 3.53 24 9.863.06 0.29 57.99 18.8 9.7 0.0162 0.2 7.3 −8 7.08 3.01 24 9.74 3.21 0.2957.91 15.7 7.3 0.0132 0.19 8.2 −9 7.08 2.8 24 15.81 3.37 0.4 62.28 14.68.1 0.0145 0.12 7.9 −8 7.38 4.03 24 15.96 3.34 0.4 62.39 21.9 8.4 0.01380.08 9.6 −11 7.68 4.43 24 15.93 3.28 0.4 62.36 24.5 10.4 0.0165 0.12 7.6−10 7.48 3.96 24 15.7 3.32 0.4 62.2 21.4 8 0.0132 0.08 7.9 −8 7.66 4.824 15.7 3.34 0.4 62.2 27 8.8 0.0138 0.03 6.3 −11 7.5 6.24 24 15.63 3.520.39 62.15 38.3 7.7 0.0116

TABLE 6 Emissions measurements from a LSB with a commercialinspirator/venturi inlet gap NOx, CO, CO2, CH4, H2, U, fraction excessNOx @ lb NOx/ mm ppm ppm % O2, % lpm lpm m/sec H2 kBtu/h air, % 3% O2MMBtu 2.7 10.7 −14 8.46 6.11 17 2.03 36 37.3 12.9 0.0186 2.7 11.9 −168.49 6.01 17 2.02 36 36.4 14.3 0.0205 2.7 13.4 −15 8.64 5.77 20.5 2.3943.4 34.5 15.9 0.0227 2.7 13.1 −15 8.56 5.93 20.5 2.42 43.4 35.8 15.70.0224 2.7 12.3 −14 8.58 5.88 26.9 3.17 57.1 35.4 14.7 0.021 2.7 13.6−15 8.69 5.7 26.9 3.13 57.1 33.9 16 0.0229 3.2 6.1 −13 7.87 7.14 27.33.51 57.9 46.8 7.9 0.0114 3.2 5.8 −14 7.77 7.33 27.3 3.56 57.9 48.7 7.70.011 3.2 5.1 −13 7.78 7.33 20.5 2.67 43.4 48.7 6.7 0.0096 3.2 5.1 −137.74 7.39 20.5 2.68 43.4 49.3 6.8 0.0097 3.2 5.1 −15 7.63 7.6 17 2.26 3651.5 6.9 0.0098 3.2 4.6 −14 7.62 7.63 17 2.26 36 51.9 6.2 0.0089 3.7 4.3−14 7.45 7.9 17 2.31 36 54.8 5.9 0.0085 3.7 3.5 −14 7.37 8.09 17 2.34 3657 4.9 0.007 3.7 4.1 −13 7.55 7.75 20.5 2.76 43.4 53.2 5.6 0.008 3.7 3.9−13 7.41 8 20.5 2.81 43.4 55.9 5.4 0.0078 3.7 4.3 −12 7.63 7.6 26.9 3.5857.1 51.5 5.8 0.0083 3.7 4.1 −12 7.65 7.58 26.9 3.58 57.1 51.3 5.50.0079 2.2 23.9 −12 9.17 4.86 26.9 2.97 57.1 27.5 26.7 0.0382 2.2 21.6−14 9.11 4.95 26.9 2.99 57.1 28.2 24.2 0.0347 1.9 31.6 −10 9.45 4.3227.1 2.89 57.5 23.8 34.1 0.0489 1.9 32.2 −8 9.44 4.32 27.1 2.89 57.523.8 34.8 0.0498 1.7 58 3 10.04 3.2 27.1 2.71 57.5 16.9 58.7 0.084 1.760 1 9.99 3.3 27.1 2.72 57.5 17.5 61 0.0874 5.1 3.6 −14 7.05 8.72 16.82.44 35.6 64.6 5.3 0.0076 5.1 3.3 −15 7.15 8.49 16.8 2.4 35.6 61.7 4.80.0068 4.1 4.8 −13 7.41 7.98 16.8 2.3 35.6 55.7 6.7 0.0095 4.1 4.3 −127.31 8.16 16.8 2.33 35.6 57.8 6 0.0087 3.7 4.6 −13 7.64 7.57 17 2.25 3651.2 6.2 0.0089 3.7 5 −14 7.39 8.01 17 2.33 36 56.1 6.9 0.01 2.9 7.2 −147.99 6.96 17 2.15 36 45 9.2 0.0133 2.9 7.2 −16 7.88 7.13 17 2.18 36 46.79.4 0.0134 3.5 5.8 −11 7.69 7.55 41.7 5.53 88.4 51 7.8 0.0111 3.5 5.4−10 7.6 7.67 41.7 5.58 88.4 52.3 7.3 0.0105 3.5 4.3 −6 7.63 7.59 56.37.48 119.3 51.4 5.8 0.0083 3.5 5.1 −4 7.72 7.4 56.3 7.37 119.3 49.4 6.80.0097 3.5 5.3 −5 7.76 7.3 56.3 7.32 119.3 48.4 7 0.01

TABLE 7 Effect of fuel staging on natural draft LSB performance totalfraction NOx NOx, CO, CO2, CH4, sec. N2, U, excess @ lb NOx/ ppm ppm %O2, % lpm fuel lpm m/sec kBtu/h air, % 3%O2 MMBtu 4.2 7 7.31 8.08 30.560 0 5.22 64.79 56.64 5.9 0.011 4.2 8 7.35 8 30.56 0 0 5.19 64.79 55.735.8 0.011 4.1 7 7.29 8.11 30.56 0 0 5.23 64.79 56.99 5.7 0.0108 9.6 −88.03 6.76 31.43 0.029 0 4.79 66.64 42.95 12.2 0.0225 11.6 −10 8.15 6.6431.35 0.026 0 4.75 66.47 41.84 14.6 0.027 10.1 −10 7.94 6.9 31.35 0.0260 4.83 66.47 44.28 12.9 0.0239 4 −1 7.32 8.08 30.56 0 0 5.22 64.79 56.645.6 0.0105 3.5 1 7.18 8.35 23.82 0 0 4.15 50.49 59.8 5 0.0094 3.7 6 7.198.33 23.82 0 0 4.15 50.49 59.56 5.3 0.0099 10.3 −10 7.92 7 24.24 0.025 03.76 51.39 45.24 13.3 0.0246 10.9 −11 8 6.84 24.24 0.025 0 3.72 51.3943.71 13.9 0.0257 11.1 −11 7.17 6.85 24.24 0.025 0 3.72 51.39 43.8 14.10.0262 3.3 2 7.17 8.37 23.64 0 0 4.13 50.11 60.04 4.7 0.0089 4 2 7.238.26 23.64 0 0 4.09 50.11 58.73 5.7 0.0106 3.4 6 7.08 8.4 21.52 0 0 3.7745.62 60.4 4.9 0.0091 3.3 4 7.02 8.46 21.52 0 0 3.78 45.62 61.12 4.70.0089 5 −7 7.19 8.3 22.12 0.028 0 3.76 46.9 59.2 7.1 0.0131 4.7 11 7.57.62 22.12 0.028 0 3.58 46.9 51.56 6.3 0.0117 4.2 −8 7.35 7.89 22.050.025 0 3.65 46.75 54.5 5.8 0.0107 4.1 −7 7.24 8.07 22.19 0.023 0.363.72 47.05 56.53 5.7 0.0106 4.1 −7 7.55 7.51 22.18 0.023 0.36 3.58 47.0350.39 5.5 0.0102 5.2 −6 7.41 7.77 29.65 0.015 0.36 4.89 62.86 53.18 7.10.0132 5.1 −7 7.52 7.55 29.64 0.015 0.36 4.82 62.84 50.81 6.8 0.0127 4.3−7 7.4 7.78 29.4 0 0.36 4.91 62.32 53.29 5.9 0.011 4.3 −8 7.43 7.75 29.40 0.36 4.9 62.32 52.96 5.9 0.011 3.9 −8 7.42 7.78 29.4 0 0 4.91 62.3253.29 5.3 0.01 4.3 −7 7.41 7.78 29.4 0 0 4.91 62.32 53.29 5.9 0.011 5.5−7 7.43 7.74 29.81 0.027 0.36 4.87 63.19 52.85 7.5 0.0138 5.3 −7 7.38.02 29.81 0.027 0.36 4.97 63.19 55.96 7.4 0.0136 4.1 −7 7.34 7.9 29.2 00.36 4.92 61.92 54.61 5.6 0.0106 3.7 −7 7.35 7.86 29.2 0 0.36 4.91 61.9254.17 5.1 0.0096 4.6 −2 7.39 7.82 29.01 0 0 4.86 61.51 53.72 6.3 0.01194.3 −5 7.23 8.13 29.01 0 0 4.97 61.51 57.22 6 0.0113 3 −6 7.1 8.36 21.870 0 3.82 46.36 59.92 4.3 0.008 3.9 −5 7.23 8.11 21.87 0 0 3.74 46.3656.99 5.5 0.0103 3.6 −5 7.16 8.24 21.87 0 0 3.78 46.36 58.5 5.1 0.00969.2 −6 8.01 6.92 15.68 0 0 2.47 33.25 44.47 11.8 0.0223 9.3 −7 8.09 6.7615.68 0 0 2.44 33.25 42.95 11.8 0.0223 12 −2 8.2 6.51 15.97 0.018 0 2.4133.87 40.66 14.9 0.0279 11 −4 8.14 6.6 15.97 0.018 0 2.43 33.87 41.4713.8 0.0257 5.5 −10 7.59 7.67 15.68 0 0 2.6 33.25 52.09 7.4 0.014 5.6 −97.62 7.62 15.68 0 0 2.59 33.25 51.56 7.5 0.0142 8.1 −8 7.75 7.33 16.060.024 0 2.55 34.05 48.53 10.7 0.0198 8.3 −3 7.79 7.28 16.06 0.024 0 2.5434.05 48.02 10.9 0.0202 8.6 −3 7.79 7.29 16.31 0.04 0 2.56 34.58 48.1211.3 0.0207 9.1 1 7.75 7.33 16.31 0.04 0 2.56 34.58 48.53 12 0.022 5.5−11 7.62 7.61 15.68 0 0 2.59 33.25 51.45 7.4 0.014 5.6 −10 7.68 7.4415.68 0 0 2.56 33.25 49.66 7.4 0.014 5.2 −9 7.58 7.55 15.68 0 1.6 2.5833.25 50.81 7 0.0131 4.5 −10 7.5 7.72 15.68 0 1.6 2.61 33.25 52.63 6.10.0115 7.5 −5 7.76 7.3 16.02 0.021 1.6 2.55 33.96 48.22 9.9 0.0183 7.4−8 7.66 7.51 15.88 0.018 1.6 2.57 33.67 50.39 9.9 0.0184 10 −1 7.8 7.2416.17 0.042 1.6 2.52 34.29 47.62 13.1 0.024 8.6 −6 7.79 7.24 16.17 0.0421.6 2.52 34.29 47.62 11.3 0.0206

We claim:
 1. A natural draft Low Swirl Burner (LSB) including an airentrainment system driven by one or more jets of fuel, wherein the fuelis introduced in such a way as to create a well-mixed fuel-air blend andestablish a flow pattern having the appropriate swirl number for the lowswirl burner into which it is introduced.
 2. The natural draft Low SwirlBurner of claim 1 wherein the appropriate swirl number is obtained usinga suitable mechanical swirler.
 3. The natural draft Low Swirl Burner ofclaim 1 wherein the appropriate swirl number is obtained byincorporating one or more fuel jets oriented axially and radially insuch manner as to establish a suitable swirl pattern.
 4. The naturaldraft Low Swirl Burner of claim 1 further including a venturi at the LSBinlet, whereby when a jet of fuel is directed into the venturi and aflow of air induced and mixed with the fuel.
 5. The natural draft LowSwirl Burner of claim 4 wherein re-circulated flue gas is injected intothe venturi of the LSB to mix with air and fuel.